1. Field of the Invention
This invention relates to tape drives that record and play tape cartridges.
2. Description of Related Art
Tape drives typically have a tape head that senses the varying magnetic fields in a tape as it passes before the head. It is industry standard to have the head parallel with the tape along the width of the tape, and to position the head sensor perpendicular to the length of the tape, so that a tape recorded on one tape drive can be played back on another drive unit. The accuracy of the head position is critical, wherein tolerances of 1/6 of a degree are common.
Present tape heads are attached to a tape drive housing by a pair of very fine set screws, such that the position of the head can be varied by turning the screws. To align the sensor to be perpendicular with the tape, an installation tape is played by the drive unit and the head is adjusted until a desirable reading is measured from the tape drive. To measure the parallelism of the head, a pair of dial indicators are mounted perpendicular to the base of the tape drive to measure the ends of the head. The screws are again turned until the gauge indicates that the head is parallel. The set screws are somewhat inaccessible because they are located next to the tape, making installation of the head very difficult. The screws are so small that the head must be further secured to the housing by glue. The glue must be applied before the head is positioned, which requires that the head be perfectly adjusted before the glue dries, adding a time constraint to an already difficult task. It would therefore be desirable to have a tape drive that would allow easy installation and alignment of the head.
Present tape drives have a stepper motor with a threaded output shaft that is coupled to the tape head through a head carrier. The head carrier has a threaded surface that follows the output shaft, such that the head moves along the width of the tape when the output shaft is rotated by the stepper motor. The translation of the carrier allows the head to sense different magnetic domains of the tape. The head carrier follows a guide pin that supports the carrier and insures that the head is not rotated relative to the tape when it is translated by the motor. The accuracy of the head location along the width of the tape is critical. For this reason the output shaft and the guide pin must be parallel, to insure that the rotation of the motor translates into a purely vertical movement of the head. Present designs have the output motor and guide pins supported at one end, wherein the shaft and pin can wobble during operation, causing a deviation in the desired movement of the head. To overcome this problem, prior devices incorporated an EPROM that would have a program to compensate for any deviations in the head. Such devices are expensive and require additional programming time which increases the complexity and cost of the tape drive. It would therefore be desirable to have a tape drive that provides a constant motor rotation to head translation ratio that can operate without an EPROM or other correction means.